Intake system for an internal combustion engine

ABSTRACT

An intake system for an internal combustion engine includes an intake manifold having a plenum connected to ambient air by a main throttle and branches leading from the plenum to an intake port of each cylinder. A storage pipe is connected and parallel with each of the intake manifold branches. Gases from an auxiliary supply are drawn by the intake manifold vacuum into the storage pipe and thence into the engine cylinders.

FIELD OF THE INVENTION

The present invention relates to an intake system of an internalcombustion engine having a plurality of cylinders, at least one intakevalve per cylinder and an intake port leading to the intake valve, theintake system comprising an intake manifold having a plenum connected toambient air by way of a main throttle and having a plurality of brancheseach leading from the plenum to an intake port of a respective one ofthe engine cylinders.

BACKGROUND OF THE INVENTION

In exhaust gas recirculation (EGR) systems, it is known to achieveimproved dynamic response to sudden changes in EGR flow by deliveringthe EGR gases directly to each intake port and avoiding the transportdelay through the plenum chamber and branches of the intake manifold asexperienced in conventional EGR. Such systems are sometimes termed“ported EGR” systems. A disadvantage of ported EGR is increased risk ofunstable combustion because a substantial segment of the intake manifoldbranch is back-filled with EGR gases during a large part of the enginecycle, forming a stratified column within the branch caused by gasesbeing drawn continuously by the prevailing manifold vacuum and storedalong the length of the branch during the period when the associatedintake valve is closed. During the intake period, this column containinga long segment of EGR gases followed by intake air is drawn sequentiallyinto the engine cylinder and unless the charge is well mixed within thecombustion chamber, isolated pockets of EGR gases may persist causingcombustion instability.

It has also been proposed to improve combustion stability by controllingthe stratification of the air and EGR gases. WO95/22687 achieves chargestratification by storing EGR gases as a column in a branch of theintake manifold. The EGR gases and the air enter the combustion chamberconsecutively and as a result the charge is vertically stratified withthe EGR gases that enter the cylinder first concentrated at the bottomof the cylinder and the air that enters last concentrated at the top.

The present invention is also concerned with an engine in which a streamof gases, such as EGR or fuel vapour, is stored as a column in theintake manifold to be drawn into the cylinder separately from the mainair charge to form a stratified charge within the engine combustionchamber.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an intake systemof an internal combustion engine having a plurality of cylinders, atleast one intake valve per cylinder and an intake port leading to theintake valve, the intake system comprising an intake manifold having aplenum connected to ambient air by way of a main throttle and having aplurality of branches each leading from the plenum) to an intake port ofa respective one of the engine cylinders, a plurality of storage pipeseach connected in parallel with a respective one of the branches of theintake manifold, each storage pipe opening at one end into the plenumand opening at the other end into the associated intake port, and aplurality of auxiliary pipes connecting an auxiliary gas supply to apoint along the storage pipe, wherein the position along the storagepipe of the connection with the auxiliary pipe is such that when theassociated intake valve is closed, gases from the auxiliary supply aredrawn by intake manifold vacuum only into the storage pipe, whereby,when the associated intake valve is subsequently opened, air from thebranch of the intake manifold and gases from the auxiliary supply storedin the storage pipe enter the cylinder as parallel streams to formwithin the cylinder stratified regions of air and gases from theauxiliary supply.

The auxiliary supply may either be a pipe connected to the exhaustsystem to supply EGR gases to the cylinders or it may be a vapour sourcederiving fuel vapours from the fuel storage tank for the engine, avapour storage canister communicating with the ullage space of the fuelstorage tank or a vapour extraction system acting to separate the fuelsupply to the engine into a liquid fraction and a vapour fraction.

In its application to recirculating exhaust gases, the present inventionmay be regarded as a variation on that in WO95/22687 and differs from itin that the EGR gases are stored in separate pipes from the intakebranches and enter the cylinders at the same time as and in parallelwith the air in the branches of the intake manifold. This allows asuperior form of stratification that better survives the compressionstroke of the piston. In the prior art, though the gases are vertically(or axially) stratified at the end of the intake stroke, they tend tomix by the end of the compression stroke. The present invention on theother hand allows radial or lateral stratification of the charge inwhich the swirling gases can remain in the same relative position evenafter compression.

The same considerations of maintaining improved stratification evenduring the compression stroke applies to engines in which the auxiliarysupply of gases is a fuel vapour supply intended to provide an easilyignitable cloud that resides in the vicinity of the spark plug gap atthe time of ignition.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, withreference to the accompanying drawing, in which:

FIG. 1 is a schematic representation of an embodiment of the inventionin which the auxiliary supply is an EGR supply and

FIG. 2 is a schematic representation of an embodiment of the inventionin which the auxiliary supply is a fuel vapour supply.

FIG. 3 is a schematic representation of an embodiment of the inventionin which two intake valves service each cylinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, an internal combustion engine 10, shown as a spark ignitionengine, has four cylinders each having an intake valve 12, an exhaustvalve 18 and a spark plug 16. The intake valve 12 is supplied with airby an intake port 14 which is connected by a pipe 15 to a plenum 22 ofthe intake manifold. The plenum 22 is connected to ambient air by way ofa main throttle 24 in the usual manner.

Each pipe 15 is divided by a wall 17 into two passages 20 and 30. Thepassages 20 are branches of the intake manifold and the passages 30 actas storage pipes for EGR gases as will now be described.

Each storage pipe 30 is connected in parallel with a respective intakebranch 20 and has one end 34 opening into the plenum 22 and the otherend 32 opening into the intake port 14. Between the ends 32 and 34, thestorage pipes are connected to EGR pipes 36 which branch from an EGRmanifold 38 that is connected by way of an EGR regulating valve 44 and apipe 42 to the exhaust manifold 40 of the engine 10. The pipes 36 areconnected nearer to the ends 32 of the storage pipes 30 that open intothe intake ports 14 but are inclined towards the ends 34 opening intothe plenum 22.

For ease of reference the cylinders of the engine will be numbered 1 to4 starting from the uppermost cylinder in the drawing as viewed. Theengine is shown with cylinder 1 during the exhaust stroke, cylinder 2during the intake stroke, cylinder 3 during the expansion stroke andcylinder 4 during the compression stroke. Cylinder 2 has an open intakevalve and air is drawn into this cylinder creating a partial vacuum inthe plenum 22. In the meantime all the other intake valves are closed.The partial vacuum in the plenum 22 results in EGR gases being drawninto the storage pipes 30 from the EGR pipe 36 for cylinders 1, 3 and 4during three of the four strokes of each cylinder when the intake valveis closed, the EGR gases being drawn into and stored in the storagepipes 30 as shown by the shaded regions in the drawing. The length ofthe storage pipe 30 should be sufficient to ensure that the EGR gasesnever spill over into the plenum 22 nor into the intake branches 20while the intake valve of the associated cylinder is closed.

As soon as the intake valve opens, as in the case of the illustratedcylinder 2, the stored EGR gases in the storage pipe 30 and air from theintake manifold branch 20 enter the cylinder at the same time and inparallel with one another, the illustrated geometry of the intake portbeing design to promote swirl or radial stratification in the cylinder,though it may alternatively be designed to promote tumble or lateralstratification. After the stored EGR gases have been exhausted, EGRgases directly from the EGR pipe 36 enter the cylinder, as shown forcylinder 2.

It can thus be seen that by storing EGR gases and allowing them to enterthe cylinders at the same time as the air, one may achieve any desiredform of stratification and one is not restricted to an axial or verticalstratification described in WO95/22687.

The EGR regulating valve 44 controls the rate at which EGR gases aredrawn from the exhaust system and therefore the proportion of EGRdilution in the cylinder. When the EGR regulating valve 44 is fullyclosed, then there is no EGR flow and the storage pipe 30 conducts air.Hence under full load operation, without the need to take any specialsteps to redirect the intake air, the full cross-section of the pipe 15becomes available for intake air and the breathing of the engine is notaffected.

The embodiment of the invention shown in FIG. 1 relates to an enginehaving only one intake valve per cylinder and in which the geometry ofthe intake port is designed to promote swirl producing radiallystratified layers across the diameter of the cylinder. It will howeverbe appreciated that the invention can also be applied to an engine inwhich the stratification is achieved by tumble having two or morevertical stratified layers across the width of the cylinder. Furthermorethe intake port leading to the intake valve may be partitioned tomaintain the separation between the parallel streams of air and EGRcloser to the intake valve.

The invention can also be applied to an engine in which each cylinderhas two intake valves supplied by a common intake port. In this case,the storage pipe 30 may be positioned to face partially or entirely oneof the intake valves while the branch 20 of the intake manifoldsupplying air to the cylinder may face the other intake valve. Thisconstruction is shown in FIG. 3, wherein valve 72 controls the flowthrough storage pipe 30 and valve 74 controls the flow through branch20.

The embodiment of the invention shown in FIG. 2 is essentially the sameas that of FIG. 1 and to avoid unnecessary repetition like parts havebeen allocated similar numbers in the 100 series. The essentialdifference lies in the fact that in place of an EGR supply pipe 42, thepipe 142 is connected to an auxiliary supply of fuel vapour. This supplycould be a vapour storage canister for evaporative emissions control,the ullage space of the fuel storage tank or a vapour extractor thatseparates the fuel supply into higher and lower boiling point fractions.As with EGR, it is desirable to achieve charge stratification but inthis case the vapour is required near the spark plug as it improvescombustion. Hence, the storage pipes 130 in FIG. 2 lead to the centresof the combustion chambers rather than their peripheries.

What is claimed is:
 1. An intake system of an internal combustion enginehaving a plurality of cylinders, at least one intake valve per cylinder,and an intake port leading to the intake valve, the intake systemcomprising: an intake manifold having a plenum connected to ambient airby way of a main throttle; a plurality of branches each leading from theplenum to the respective intake port of a respective one of the enginecylinders; a plurality of storage pipes each connected in parallel witha respective one of the branches of the intake manifold, each storagepipe opening at a first end into the plenum and opening at a second endinto the associated intake port; a plurality of auxiliary pipesconnecting an auxiliary gas supply at a respective position along eachof the storage pipes, each of the positions along each of the storagepipes of the connection with the auxiliary pipe is such that when theassociated intake valve is closed, a portion of the gas from theauxiliary supply is drawn by an intake manifold vacuum only into thestorage pipe, and when the associated intake valve is subsequentlyopened, air form the associated branch of the intake manifold and thegas from the auxiliary supply stored in the storage pipe enter thecylinder as parallel streams to form stratified regions of air and gasesfrom the auxiliary supply within the cylinder.
 2. An intake system asclaimed in claim 1, wherein the auxiliary gas supply comprises an EGRpipe connected to the engine exhaust system and operative to supplyexhaust gases for recirculation to the intake system.
 3. An intakesystem as claimed in claim 1, wherein the auxiliary gas supply comprisesa pipe connected to a fuel vapor source.
 4. An intake system as claimedin claim 3 where wherein the end of each auxiliary pipe opening into astorage pipe is inclined to the axis of the storage pipe to direct thegases from the auxiliary supply towards the plenum of the intakemanifold.
 5. An intake system as claimed in claim 4, wherein the end ofeach auxiliary pipe opening into a storage pipe is inclined to the axisof the storage pipe to direct the gases from the auxiliary supplytowards the plenum of the intake manifold.
 6. An intake system asclaimed in claim 5, wherein the end of each auxiliary pipe opening intoa storage pipe is inclined to the axis of the storage pipe to direct thegases from the auxiliary supply towards the plenum of the intakemanifold.
 7. An intake system as claimed in claim 6, wherein each of theauxiliary pipes comprise branches of a manifold having a common plenumconnected to the auxiliary supply by way of a flow regulating valve. 8.An intake system as claimed in claim 7, wherein each of the auxiliarypipes comprise branches of a manifold having a common plenum connectedto the auxiliary supply by way of a flow regulating valve.
 9. An intakesystem as claimed in claim 8, wherein each of the auxiliary pipescomprise branches of a manifold having a common plenum connected to theauxiliary supply by way of a flow regulating valve.
 10. An intake systemas claimed in claim 9, wherein each of the auxiliary pipes comprisebranches of a manifold having a common plenum connected to the auxiliarysupply by way of a flow regulating valve.
 11. An intake system asclaimed in claim 10, wherein the storage pipes are formed providing aportion in the branches lading from the plenum to the intake ports, apassage to a first side of each of the partitions each comprising thebranches of the intake manifold and a passage to the second side of eachof the partitions each comprising the storage pipes.
 12. An intakesystem as claimed in claim 11, wherein the storage pipes are formedproviding a portion in the branches lading from the plenum to the intakeports, a passage to a first side of each of the partitions eachcomprising the branches of the intake manifold and a passage to thesecond side of each of the partitions each comprising the storage pipes.13. An intake system as claimed in claim 12, wherein the storage pipesare formed providing a portion in the branches lading from the plenum tothe intake ports, a passage to a first side of each of the partitionseach comprising the branches of the intake manifold and a passage to thesecond side of each of the partitions each comprising the storage pipes.14. An intake system as claimed in claim 13, wherein the storage pipesare formed providing a portion in the branches lading from the plenum tothe intake ports, a passage to a first side of each of the partitionseach comprising the branches of the intake manifold and a passage to thesecond side of each of the partitions each comprising the storage pipes.15. An intake system as claimed in claim 14, wherein the storage pipesare formed providing a portion in the branches lading from the plenum tothe intake ports, a passage to a first side of each of the partitionseach comprising the branches of the intake manifold and a passage to thesecond side of each of the partitions each comprising the storage pipes.16. A intake system as claimed in claim 15, for use with an enginehaving a first and second intake valve per cylinder supplied by a commonintake port, further comprising the storage pipes and the intakemanifold branches each having comparable flow cross-sectional areas,each of the storage pipes facing the first intake valves and each of theintake manifold branches facing the second one of the intake valves,respectively.
 17. An intake system as claimed in claim 16, for use withan engine having a first and second intake valve per cylinder suppliedby a common intake port, further comprising the storage pipes and theintake manifold branches each having comparable flow cross-sectionalareas, each of the storage pipes facing the first intake valves and eachof the intake manifold branches facing the second one of the intakevalves, respectively.
 18. A intake system as claimed in claim 17, foruse with an engine having a first and second intake valve per cylindersupplied by a common intake port, further comprising the storage pipesand the intake manifold branches each having comparable flowcross-sectional areas, each of the storage pipes facing the first intakevalves and each of the intake manifold branches facing the second one ofthe intake valves, respectively.
 19. A intake system as claimed in claim18, for use with an engine having a first and second intake valve percylinder supplied by a common intake port, further comprising thestorage pipes and the intake manifold branches each having comparableflow cross-sectional areas, each of the storage pipes facing the firstintake valves and each of the intake manifold branches facing the secondone of the intake valves, respectively.
 20. An intake system as claimedin claim 19, for use with an engine having a first and second intakevalve per cylinder supplied by a common intake port, further comprisingthe storage pipes and the intake manifold branches each havingcomparable flow cross-sectional areas, each of the storage pipes facingthe first intake valves and each of the intake manifold branches facingthe second one of the intake valves, respectively.
 21. An intake systemas claimed in claim 20, for use with an engine having a first and secondintake valve per cylinder supplied by a common intake port, furthercomprising the storage pipes and the intake manifold branches eachhaving comparable flow cross-sectional areas, each of the storage pipesfacing the first intake valves and each of the intake manifold branchesfacing the second one of the intake valves, respectively.